As properties required for an electrophotographic toner used in an image formation apparatus, such as a color copier or a color printer using an electrophotography method, there are cited: color reproduction quality, transparency of an image and lightfastness. Widely used electrophotographic toners in the present time contain a pigment as a colorant which is dispersed in a particle. Since they use pigments, it is excellent in lightfastness. However, since the colorant is insoluble, it is likely to be aggregated to result in the problems of decrease of transparency and color shift of the transmitted color. Therefore, there are disclosed toners in which the colorant in the toners is changed from a pigment to a dye (for example, refer to Patent document 1). Although these toners are excellent in transparency and color shift, they have conversely a problem of lightfastness. Further, since commonly known general dyes have relatively low molecular weight, it will sublimate during the step of heat fixing, and they had the defects of causing: staining of a fixing roller surface and an inside of the printer, decrease of an image density; and a smear. In recent years, a toner which uses a metal complex as a colorant is disclosed in order to resolve such defects (for example, refer to Patent document 2). Although the above-mentioned toner containing the metal complex colorant was excellent in lightfastness, the solubility of the colorant was too low to produce a different reflectance after printing owing to aggregation of the colorant. Consequently, further improvement was desired.
These problems were greatly improved by employing an electrophotographic toner using a metal-containing compound (for example, refer to Patent document 3). The image acquired from this toner was excellent in color reproduction quality and lightfastness, and it was extremely good.
An electrophotographic toner is generally produced by the knead-pulverizing method of: melt-kneading a mixture of a binder resin and a pigment, and according to necessity, with a releasing agent such as a wax and a charge controlling agent; fine grinding the mixture; and further size classifying the particles.
The toner produced by the usual knead-pulverizing method has an amorphous shape with broad particle size distribution and have the problems of: low fluidity, low transferring property, requiring high fixing energy, uneven electric charging amount among toner particles, and low electric charging stability. Furthermore, the image quality of the image acquired from such toner was still to be improved.
On the other hand, in order to overcome the problems of the above-mentioned toner produced by the knead-pulverizing method, the production method of the toner by the polymerizing method is proposed. Since this method does not include the pulverizing step, it does not need a knead manufacturing process and a pulverizing step for production of that toner, as a result, its contribution to cost reductions achieved by energy saving, abbreviation of production time, and improvement in a product yield are large. Moreover, it is easy to achieve a sharp particle size distribution of the toner particles by the polymerizing method compared with the particle size distribution of the toner particles by the knead-pulverization method. In addition, it is easy to incorporate a wax inside of the toner particles, and the fluidity of the toner can be raised largely. Moreover, it is also easy to obtain spherical toner particles.
However, the toner produced by the polymerizing method has many problems which are not yet resolved. For example, even if the toner obtained by the above-mentioned method is washed at the time of production, a surfactant remains to toner particles. Therefore, when the toner is used or kept under high-temperature and high humidity or, the toner particles absorb moisture, electric charging rise dup property and electric charging stability will be decreased. As a result, there will be produced white spots on an image or a fog, and dot reproducing ability and fine-line reproducing ability will fall, and image quality will be deteriorated. In particular, white spots on an image or a fog appeared remarkably when a full color image was produced by laminating a plurality of toner images (for example, refer to Patent document 4).
From the background described above, it has been requested a toner which fully satisfies color reproduction quality and lightfastness, and excellent in water fastness and electric charging stability without white spots of an image.